1. Field of the Invention
The present invention relates to a nonvolatile semiconductor memory device and a method of manufacturing the same, and more specifically, is applied to a nonvolatile semiconductor memory device having grooves insulated by insulating films between floating electrodes of adjacent nonvolatile memory elements, and to a method of manufacturing the same.
2. Description of the Related Art
As a conventional nonvolatile semiconductor memory device having floating electrodes, there is a device as shown in FIG. 17 (for example, Jpn. Pat. Appln. KOKAI Publication No. P2002-016154). The nonvolatile semiconductor memory device shown in FIG. 17 comprises a silicon substrate 111, a gate oxide film 112, a first polycrystalline silicon film 113 which is a lower layer floating electrode, a silicon oxide film 116, a silicon oxide film 117 which is an STI filling material for an element isolation region, a second polycrystalline silicon film 118 which is an upper layer floating electrode, an ONO insulating film (a three-layer film of a silicon oxide film, a silicon nitride film, and a silicon oxide film) 119, a third polycrystalline silicon film 120 which is a lower layer control electrode, a WSi film 121 which is an upper layer control electrode, and a silicon oxide film 122 which is an insulating protective film.
The first polycrystalline silicon film 113 which is the lower layer floating electrode is insulated from the lower floating electrode, to which a cell which is adjacent thereto corresponds, by the silicon oxide films 116, 117 at the element isolation region. The second polycrystalline silicon film 118 which is the upper layer floating electrode is isolated from the upper floating electrode, to which a cell which is adjacent thereto corresponds, by a groove 126 on the silicon oxide film 117. The floating electrode 118 and the control electrode 120 are isolated by the ONO insulating film 119 which is an interelectrode insulating film.
However, the conventional nonvolatile semiconductor memory device is structured such that the control electrode 120 along with the ONO insulating film 119 enters the interior of the groove 126 between the adjacent cells at this floating electrode corner portion 125.
Therefore, electric fields converge at the floating electrode corner portion 125, and the insulating characteristic of the ONO insulating film 119 at this corner portion 125 deteriorates. Thus, there is the problem that the characteristic of maintaining the electric charges injected in the floating electrodes 113, 118 in accordance with stored information is poor.